Project Summary/Abstract Acute pancreatitis is a common, life-threatening disorder of the pancreas. Abnormal acinar cell Ca2+ signals play a crucial role in initiating this disease. We have previously shown that abnormally elevated Ca2+ signals in the basal region are associated with pathologic intra-acinar protease activation, an early and critical event in the development of pancreatitis. This Ca2+ signal is mediated by an endoplasmic reticulum (ER) Ca2+ channel, the ryanodine receptor (RyR). In this proposal, we examine mechanisms that regulate this pathologic RyR Ca2+ release in the acinar cell. We have shown that increasing cAMP in acinar cells causes RyR phosphorylation, RyR Ca2+ release, and enhanced protease activation1, 2. In preliminary work, we demonstrate that alcohol, a leading cause of pancreatitis, triggers cAMP-mediated RyR phosphorylation as well as RyR Ca2+ release and enhanced protease activation. Therefore, we hypothesize that intra-acinar protease activation and pancreatitis, particularly that induced by alcohol exposure, are triggered by release of acinar cell Ca2+ from pathologically activated, phosphorylated RyRs. In this proposal, using a combination of novel genetic and pharmacologic tools, we will, in the presence or absence of alcohol, pursue the following Specific Aims: (1) Examine whether RyR phosphorylation causes RyR Ca2+ release in isolated acini (2) Study whether RyR phosphorylation and RyR Ca2+ release predispose to protease activation in isolated acini (3) Determine whether RyR phosphorylation and RyR Ca2+ release predispose to protease activation and pancreatitis in vivo. The effects of phosphorylation on RyR sites thought to mediate PKA-dependent RyR Ca2+ release will be directly tested using previously generated transgenic mice that harbor phospho-mimetic or phospho-resistant mutations in the RyR PKA phosphorylation site. It is anticipated that these studies on the role of the RyR in pathologic protease activation and pancreatitis will (1) lead to improved understanding of aberrant Ca2+ signaling in pancreatitis, (2) provide a novel link between alcohol and RyR Ca2+ release that may have broader implications for mechanisms contributing to alcohol's complications in multiple other organ systems, and (3) suggest treatment strategies that target the RyR in the pancreas.